In inks for oily marking pens, there have been used solvents such as xylene, methyl cellosolve and the like which have a good solubility to oil-soluble dyes, but these solvents are odorous and poisonous and so they are devoid of safety to human beings. For this reason, the usage, use circumstances and the like of these solvents are required to be restricted and limited.
In order to solve these problems, there has been developed, in recent years, an alcoholic ink mainly comprising a less odorous and less poisonous alcoholic solvent, particularly an ink for marking pens (hereinafter referred to as "ethanol-based ink") in which ethanol is used as a main solvent.
However, in this kind of ethanol-based ink, a dye is insoluble, and even if soluble, the dye precipitates during a long period of time, which means that the ink is poor in stability with time, because among organic solvents, ethanol has a relatively low solubility to the dye and a resin, and the oil-soluble dye which has been heretofore used in the marking pens contains a few functional groups having an interaction with ethanol. Hence, a dye is now desired which is compatible with ethanol and an ethanol-soluble resin for use in the ink.